... systems

Some of them are microquasars (for details see, for example, Greiner 1999; Mirabel 2000; Mirabel & Rodriguez 2002).

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... frame

We use as usual the notation $r_{\rm g}=2GM/c^2$.

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...(Cherepashchuk 2002)

Shakura (1972) predicted that if the plane of an accretion disk is tilted relative to the orbital plane of a binary system, the disk can precess.

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